1. Field of the Invention
The invention relates to an image forming apparatus.
2. Description of the Related Art
An image forming apparatus such as copying machine and printer is designed to transfer toner and ink on a recording paper, and discharge it out of the machine and stack up on a tray. An image forming apparatus of electrophotographic system for transferring the toner on the paper comprises a heat-fixing device for thermally fixing the toner on the paper while gripping and conveying the paper on which the toner is transferred between contacting parts of a heating roller having a heater inside and a pressure roller.
The heating roller of the heat-fixing device is heated closely to 200° C., and so-called VOC (volatile organic compounds) gas may be generated from the heat-fixing device. Typical examples of VOC include alcohol, toluene, benzene, and styrene. That is, VOC is a generic name of organic compounds having volatile properties. An example of VOC gas generated from the heat-fixing device is methyl mercaptan generated from silicone oil used in the heating roller. When a styrene-based resin material is used in the thermal fixing device or its neighboring parts, styrene is generated from the resin material. Silicone oil and resin material hardly generate VOC gas at room temperature, but when heated, components are partly vaporized (or the VOC gas contained as fine bubbles in the material is expanded), and VOC gas may be generated.
Such VOC gas is not always a serious problem, but it becomes a problem even if a slightest malodor is contained or type of gas regulated by emission control law is generated. Methyl mercaptan belongs to the former type, and styrene belongs to the latter type. It has been hence proposed to remove VOC gas by providing the image forming apparatus with a filter (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-161122).
JP-A No. 11-161122 discloses an apparatus for decomposing ozone generated in charger and charge removing device and mercaptan generated in fixing device by reaction, and discharging emission gas containing decomposition gas out of the apparatus.
It is also proposed to mix the ozone generated in the apparatus and air containing VOC, and to decompose the VOC by oxidation reaction (see, for example, JP-A No. 6-19264).
According to the above-descried conventional image forming apparatus, the VOC gas generated in: the apparatus can be removed by the catalytic filter. However, the VOC gas is generated also from the toner and paper, and is also generated continuously for a specific time from the paper on which the image is formed discharged outside of the apparatus (until the paper is cooled to specified temperature).
The VOC gas generated from the toner and paper is not so serious as to have adverse effects on human health, and does not release any peculiar malodors.
However, by color processing of image forming apparatus (increase of used amount of color toners) and high speed processing, the amount of VOC gas generated from the toner and paper tends to increase. Further more, the variety of paper used by recent users is diversified, and a large amount of VOC gas may be generated in future depending on the type of paper.
As the VOC gas increases, the smell may be regarded as a problem by the user if adverse effects are not caused on human health. Considering the recent trend of enforcing regulations of environmental law, the output of VOC gas may exceed the reference value.
In consideration of these backgrounds, in future, it may be required to remove VOC gas generated from paper and toner. In the conventional image forming apparatus, the VOC gas generated from the output paper is released into the space outside of the apparatus.